Olive-sided flycatcher? (1 Viewer)

I was in the vicinity of the Philadelphia Museum of Art today and I heard three "phip" sounds in a row. This was repeated, but always as a triplet of the same sound. The bird making the noise was alone in the top of a bare tree and was about 6-8 inches. I didn't have my optics, but the bird was greyish with a darker slight crest. Olive-sided flycatcher? Is there anything else that fits this description?

Olive-sided Flycatcher? Not this time of year! Don't know what it could be though - I'm not very good at ID via description.

Right, I hear you with the timing comment. I think the bird's call seems to be the most salient feature. Anyone know which other birds make a similar call?

Not enough to go on really, but American Robins make a similar call. I would call it a "see, pip, pip, pip" or "see, pup, pup, pup" noise. Sometimes all you hear is the "pup" sound when they fly overhead or are perched.

Here's a link. Listen to the call and see if that might be it:
http://www.mbr-pwrc.usgs.gov/id/framlst/i7610id.html